Search Results (862)

Background: In 2019, a new virus caused by SARS-CoV-2, called COVID-19, spread throughout the world, causing a pandemic state. As the pandemic progressed and cases continued to increase, safe vaccines were developed for the entire population. In Brazil, AstraZeneca^® (ChAdOx1-S) and Pfizer^® (BNT162b2) vaccines were among those administered to the population. Objectives: The objective of this study was to analyze whether immunoglobulin G (IgG) is produced for COVID-19 in individuals immunized with two doses of AstraZeneca (ChAdOx1-S) and Pfizer (BNT162b2) vaccines and to evaluate several parameters in order to understand how our bodies respond to this immunization. Methods: The study involved the participation of 120 individuals: 49 in the control group, 44 vaccinated with the AstraZeneca vaccine, and 27 the vaccinated with Pfizer vaccine. Results: Hematological, biochemical, inflammatory, and oxidant/antioxidant parameters and the production of IgG antibodies were analyzed. An increase in some inflammatory parameters was observed in vaccinated individuals, which may have been caused by an immune reaction after vaccination. In terms of hematological parameters, the changes caused by vaccination appear to be transient and quickly resolved after immunization. In terms of biochemical parameters, an increase in IgG antibodies was observed in the group vaccinated with the Pfizer^® vaccine; however, the AstraZeneca^® and control groups also produced IgG, although to a lesser extent. In terms of the remaining parameters, there was little change after vaccination. Regarding the levels of oxidants/antioxidants, it was observed that there was a compensation by antioxidants due to the increase in oxidant parameters, which may act as corrective mechanism. Conclusions: Both the AstraZeneca^® and Pfizer^® vaccines induced anti-SARS-CoV-2 IgG production, accompanied by inflammatory, hematological, and oxidative changes. Full article

Background: The development of safe and effective vaccines against SARS-CoV-2 was crucial for controlling COVID-19 and establishing long-lasting immune memory in the population. Methods: This study evaluated cellular immune memory in individuals vaccinated with different regimens in Rio Grande do Sul using flow cytometry. Additionally, the rs2228059 polymorphism in the IL15RA gene was genotyped. A total of 62 participants were randomly recruited. Results: A decrease in memory T cell subsets in response to SARS-CoV-2 stimuli was observed in total CD3⁺, CD4⁺, and CD8⁺ T cells. Regarding the timing of the last vaccine dose, 94.4% of participants had received their final COVID-19 vaccination at least two years prior to recruitment. The rs2228059 polymorphism was genotyped in 443 individuals from the Rio Grande do Sul population. Among participants who received the ChAdOx1/ChAdOx1/BNT162b2 vaccination regimen and carried the TT genotype, an increase in CD8⁺ naive, CD8⁺ effector and CD4⁺ naive subsets was observed in stimulated cells. Although preliminary, the results suggest no major differences between vaccination regimens. Conclusions: The progressive reduction in memory T cell counts supports the need for booster doses, which is essential not only in the context of new emerging variants but also especially to maintain adequate cellular immune protection. Full article

Background/Objectives: To estimate (a) survival after SARS-CoV-2 infection by COVID-19 vaccination status, and (b) COVID-19 vaccine effectiveness in a middle-income country. Methods: In this retrospective cohort study, secondary analysis of data from the national surveillance and vaccination databases was conducted. The primary outcome was COVID-19 death classified based on the WHO criteria. Data were analysed by vaccination status, age, sex, geographic region, and wave period. Kaplan–Meier curves were plotted; log-rank followed by multiple comparison tests were used to compare survival probabilities. Cox proportional-hazards models with time-varying covariates estimated hazard ratios (HR). Vaccine effectiveness was computed as (1-HR) × 100. Results: A total of 55,299 COVID-19 cases were captured by the national surveillance system between 1 April and 31 December 2021. Of these, 45,774 (1581 vaccinated, 44,193 unvaccinated) were included in the analysis. After a follow-up of 327 days, there were 22 deaths (case fatality rate (CFR) 1.5%) among 1581 COVID-19 vaccinated cases and 1821 deaths (CFR 4.1%) among 44,193 unvaccinated cases. There was one COVID-19 death per 10,000 person days in vaccinated cases compared with 2.7 COVID-19 deaths per 10,000 person days in unvaccinated cases. After adjustment for age, sex, and geographic region, the effectiveness against COVID-19 death across all vaccine types (ChAdOx1 nCoV-19, BNT162b2, Ad26.COV2.S, or BBIBP-CorV) was 68% (95% CI: 51–79). Effectiveness was 75% (95% CI: 59–84) for ChAdOx1 nCoV-19. Vaccine effectiveness across all vaccine types was higher in younger cases, (82% (95% CI: 52–93), 18–64 years vs. 63% (95% CI: 41–77), ≥65 years), females (84% (95% CI: 63–93), females vs. 53% (95% CI: 24–71), males) and those vaccinated in the past 3 months (71% (95% CI: 47–85), past 0–3 months vs. 56% (95% CI: 23–75), 3–6 months). Conclusions: COVID-19 vaccines were effective in preventing COVID-19 death in a population with low vaccination coverage. Limitations of the analysis include the use of surveillance data (under-reporting of cases, missing data), exclusion of partially vaccinated cases, and insufficient data on important confounders (circulating variants and comorbidities). Full article

Background: The COVID-19 pandemic accelerated the development of diverse vaccine platforms, including mRNA, adenoviral vector, and protein subunit vaccines. Given the growing evidence that the gut microbiome modulates vaccine-induced immunity, this study compared the effects of a protein subunit vaccine (NVX-CoV2373), an mRNA vaccine (BNT162b2), and an adenoviral vector vaccine (ChAdOx1) on gut microbiome diversity following booster vaccination. Methods: We conducted a prospective cohort study involving 35 healthy adults who received an NVX-CoV2373 booster. Stool and blood samples were collected before vaccination and three weeks afterward. Gut microbiome profiles were analyzed using 16S rRNA gene sequencing, and the results were compared with our previous cohorts who received BNT162b2 or ChAdOx1 vaccines. Results: The NVX-CoV2373 booster was associated with a significant increase in the Shannon diversity index (p = 0.027), indicating enhanced alpha diversity. This finding contrasts with the decrease or absence of significant short-term change observed following repeated administrations of adenoviral vector and mRNA vaccines, respectively. Notably, NVX-CoV2373 vaccination was accompanied by an increased relative abundance of beneficial taxa such as Bacteroides fragilis and a decrease in Prevotella bivia. In comparison, repeated ChAdOx1 doses resulted in a sustained reduction in alpha diversity, whereas BNT162b2 showed a transient post-booster rise followed by a long-term decline in species richness. Conclusions: In the booster setting, the protein subunit vaccine NVX-CoV2373 exerted a distinct and favorable effect on gut microbiome diversity, increasing alpha diversity in contrast to the patterns observed with mRNA and adenoviral vector booster vaccines. Full article

Background/Objectives: Paediatricians’ recommendations influence parental decisions to vaccinate their children. On 19 January 2022, the World Health Organization authorized the Pfizer-BioNTech COVID-19 vaccine (BNT162b2) under Emergency Use Listing for children under 12 years as a measure to mitigate disease spread and direct protection for children with underlying conditions. We assessed knowledge, attitudes, and practices (KAP) of Palestinian paediatricians regarding COVID-19 vaccination for children under 12 years and identified factors affecting support for vaccination. Methods: From 1 October to 8 November 2023, we surveyed paediatricians across the West Bank using structured telephone interviews. We collected data on sociodemographic characteristics and KAP regarding COVID-19 vaccination and calculated KAP scores from eight, nine, and nine items, respectively, with total scores categorized as poor/moderate/good. We performed bivariable and multivariable analyses to identify factors associated with paediatricians supporting COVID-19 vaccination for children under 12 years. Results: Of the 367 eligible paediatricians, 323 (88%) responded; the median age was 51 years (range: 28–70); 27% supported COVID-19 vaccination for children. Mean scores for knowledge (range 0–8), attitude (0–9), and practice (0–9) were 3.0 ± 2.1, 3.9 ± 2.4, and 4.0 ± 1.7, respectively. The mean overall KAP score (0–26) was 11 ± 4.8. Safety and efficacy concerns and lack of long-term data were the main reasons for hesitancy. Higher knowledge scores (PR = 1.8, 95% CI: 1.3–2.5, p = 0.001) and positive attitudes (PR = 1.6, 95% CI: 1.1–2.3, p = 0.01) were significantly associated with paediatricians’ support for vaccination. After adjustment for other factors, participants with regular continuing medical education attendance (aPR = 1.4, 95% CI: 1.0–2.6, p = 0.045), trusting WHO recommendations (aPR = 3.1, 95% CI: 1.4–7.8, p = 0.047), having a positive attitude score (aPR = 1.3, 95% CI: 0.4–4.4, p = 0.041), and a good total KAP score (aPR = 1.1, 95% CI: 1.0–1.2, p = 0.044) supported COVID-19 vaccination for children. Conclusions: Support for COVID-19 vaccination among Palestinian paediatricians was low, associated with their knowledge, attitudes, and trust in health authorities. The revised WHO recommendations from 10 November 2023, decreasing the priority of vaccinating healthy children, could influence the opinion of paediatricians. However, the low support for COVID-19 vaccinations could affect the performance of other vaccination programmes and should be carefully addressed through targeted education. Full article

Background: Healthcare workers (HCWs) are at high risk of breakthrough SARS-CoV-2 infections despite complete vaccination schedules. There are gaps in our understanding of the specific antibody isotypes and cytokine profiles produced during an infection following vaccination. In this study, we evaluated SARS-CoV-2⁻specific antibody isotypes and their association with cytokine production in HCWs with breakthrough infections. Methods: Serum samples from 114 HCWs were analyzed for antibody isotypes against the nucleoprotein (NCP) and the receptor binding domain (RBD) of the spike protein, as well as for a panel of 13 cytokines. Results: Vaccinated SARS-CoV-2⁺ HCWs showed a higher prevalence of anti-SARS-CoV-2 antibodies against NCP (IgM = 93.8%, IgG = 93.8%, IgA = 28.1%) and RBD (IgM = 46.9%, IgG = 100%, IgA = 90.6%). A specific IgM response to NCP was more frequent in vaccinated SARS-CoV-2⁺ individuals, whereas IgA responses were predominantly specific for RBD. Both pro- and anti-inflammatory cytokines were elevated in vaccinated HCWs with breakthrough infections compared with unvaccinated and uninfected individuals. Interestingly, infected IgG+ HCWs with IgM specific for both NCP and RBD exhibited significantly higher IL-8, IL-6, TNF-α, IFN-γ, IL-2, IL-10, and TGF-β concentrations. Conclusion. Our data show that breakthrough infections in vaccinated HCWs induce a robust pro-and anti-inflammatory cytokine profile, which is associated with a broader IgM response directed against both NCP and RBD. Full article

Introduction: The COVID-19 pandemic posed additional challenges for this vulnerable population, such as Sjögren’s disease (SjD), underscoring the need for effective and safe vaccination strategies. Objective: To evaluate the immunogenicity and safety of COVID-19 vaccines in patients with SjD. Methods: This prospective, observational, longitudinal study included SjD patients from the SAFER cohort. Immunogenicity was assessed via anti-spike IgG (IgG-S) titers using chemiluminescence reported as geometric mean titers (GMT) and fold increase in GMT (FI-GMT). Disease activity was evaluated using the ESSDAI score. Adverse events and COVID-19 infections were also monitored. Assessments were conducted at four time points: pre-first dose (T1), pre-second dose (T2), pre-booster (T3), and four weeks post-booster (T4). Primary vaccination involved ChAdOx1 nCoV-19 or inactivated vaccine (CoronaVac), and boosters were either homologous (ChAdOx1 nCoV-19) or heterologous (BNT162b2). Results: Among 51 participants (mean age 46 years; 90% female), 41% had comorbidities and 27% (n = 14/51) were highly immunosuppressed. Among those 73% (n = 37/51) under low immunosuppression, n = 8/51 (13%) were not using any medication. At baseline, 11% (n = 4/35) showed moderate/high disease activity, which decreased to 6.5% (n = 2/31) at T4. Primary vaccination was ChAdOx1 in 94% (n = 48/51) and CoronaVac in 6% (n = 3/51); 73% (n = 37/51) received heterologous and 27% (n = 14/51) homologous boosters. COVID-19 infection post-booster occurred in 20% (n = 10/51). Seroconversion rates reached nearly 100% across all medication subgroups except for biologic users, who showed delayed but stable seroconversion by T4. IgG-S titers increased progressively through T4. Primary immunization induced an ascending GMT in both vaccine types. At T4, the GMT was significantly higher in the BNT162b2 group (2148.03 [1452.05–3155.84]; p < 0.001; 95% CI) than in the ChAdOx1 group (324.29 [107.92–974.48]; p < 0.001; 95% CI); the fold-increase in immune response was six times greater with BNT162b2 (5.98 [2.97–12.03]; p = 0.001; 95% CI). Seroconversion was 100% in the heterologous group versus 83% in the homologous group (p > 0.01). Those with prior infection showed significantly higher titers, particularly at T2 and T3 (p < 0.001 for T1–T3). Adverse events were mild and not statistically significant. Multivariate regression confirmed BNT162b2 as an independent factor for higher antibody titers. Conclusion: COVID-19 vaccination in patients with SjD was safe and induced high anti-spike antibody titers and seropositivity. Heterologous boosting, particularly with BNT162b2, demonstrated superior immunogenicity. No association was found between vaccination and SjD disease flares or worsening activity. Full article

Background: Numerous studies have proved the efficacy of vaccination in reducing Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) transmission and the coronavirus disease (COVID-19) burden. However, even though the COVID-19 vaccination coverage is high for primary doses, a booster dose is needed to sustain protection. Continuing our previous research, this study evaluates the immunogenicity and safety of full and half doses of two COVID-19 booster vaccines, ChAdOx1-S (AstraZeneca) and BNT162b2 (Pfizer-BioNTech), in individuals primed with ChAdOx1-S. Methods: This study was an observer-blind randomized controlled trial to evaluate the immunogenicity and safety of half and full doses of two COVID-19 booster vaccine types, BNT162b2 and ChAdOx1-S, among fully vaccinated, ChAdOx1-S-primed individuals in Jakarta, Indonesia. A total of 329 participants were randomized to receive either full or half doses of the booster vaccines, namely the ChAdOx1-S and BNT162b2 COVID-19 vaccines. Immunogenicity was assessed through SARS-CoV-2 antibody titers and neutralizing antibodies (NAbs) at 28 days post-booster, while safety was monitored via adverse event reporting. Results: The results showed that both vaccines demonstrated increased geometric mean titers (GMTs) post-booster. In the ChAdOx1-S booster group, at the baseline visit (day 0) and third visit (day 28), no statistically significant differences in GMT between the half- and full-dose groups were observed (p = 0.970 and 0.539, respectively). In the BNT162b2 group, no statistically significant difference was noted at the baseline visit, while the full dose was higher than the half dose at 28 days (Day 28, p = 0.011). Surrogate virus neutralization tests (sVNTs) and NAbs assays also revealed no significant differences between the half and full dose groups for both the Wuhan strain and the Delta variant. The BNT162b2 group compared to the ChAdOx1-S group revealed a statistically significant increase in IgG levels compared to ChAdOx1-S, with p-values of <0.001 and <0.001 for the half dose and full dose, respectively. This was also reflected in the NAbs test results, where BNT162b2 showed significantly higher levels against both the Wuhan strain and Delta variant. Adverse events were predominantly mild: 79.6% (n = 86/108) in the ChAdOx1-S full-dose group, 75.4% (n = 43/57) in the ChAdOx1-S half-dose group, 84.2% (n = 101/120) in the BNT162b2 full-dose group, and 92.6% (n = 88/95) in the BNT162b2 half-dose group, with pain at the injection site being the most common local reaction and myalgia and headache the most frequent systemic reactions. One serious adverse event was reported, assessed as unrelated to the vaccine. Conclusions: This study confirms that half doses of ChAdOx1-S and BNT162b2 are as immunogenic and safe as full doses, and a heterologous booster is more immunogenic than a homologous booster. Full article

Standardized, one-size-fits-all COVID-19 booster schedules may be suboptimal due to individual variation in immune backgrounds, particularly prior infection, which induces robust hybrid immunity. This study estimated optimal booster timing by modeling antibody decay in relation to surrogate correlates of protection (CoP). In a prospective cohort of 177 Japanese healthcare workers, we longitudinally monitored anti-spike receptor-binding domain (S-RBD) antibody titers following BNT162b2 vaccination. Participants were stratified into SARS-CoV-2-naïve and previously infected groups. Mixed-effects models were developed to predict when antibody titers would decline below predefined CoP thresholds. The model estimated optimal booster timing after a two-dose primary series to be 3–5 months for naïve individuals and approximately one year for those with prior infection. Following a third dose, the estimated interval extended to 8–12 months for the naïve group and 1.5–2 years for the previously infected group. These substantial differences underscore the limitations of uniform booster schedules. Our findings provide a quantitative framework for personalized vaccination strategies based on individual antibody profiles and immune status, thereby optimizing protection. Full article

Background/Objectives: The COVID-19 vaccines have been extensively studied for their potential adverse side effects. However, reports of unexpected but potentially beneficial immune responses have received comparatively less attention. Methods: In this case series, a PubMed search was conducted using the terms “warts”, “verruca”, “HPV”, “COVID-19”, “SARS-CoV-2”, “immunization”, and “vaccination.” All reported cases of wart clearance temporally linked to COVID-19 vaccination were identified and summarized, including patient demographics, vaccine type, number of doses, timing of clearance, and follow-up duration. Results: Five cases were identified. Patients varied in age, sex, comorbidity, and immunologic status. Warts were long-standing and treatment-resistant in all cases. Clearance occurred within approximately 2–4 weeks following the second or third vaccine dose (either mRNA-based [BNT162b2, mRNA-1273] or adenoviral vector [ChAdOx1-S]) and was sustained for 2–8 months of follow-up with no recurrences reported. Conclusions: While causality cannot be determined, the convergence of reports across diverse patients, consistent timing of clearance, and plausible immunologic pathways suggest that COVID-19 vaccination may, in rare instances, trigger beneficial immune activation against HPV-infected keratinocytes. Recognition of such unexpected outcomes underscores the need for broader vaccine safety and efficacy surveillance that includes both adverse and beneficial immune effects. Full article

Background: To prospectively evaluate the safety and clinical impact of SARS-CoV-2 vaccines in patients with systemic lupus erythematosus (SLE). Methods: Subanalysis of the Brazilian multicenter observational study “Safety, Effectiveness and Duration of Immunity after Vaccination against SARS-CoV-2 in Patients with Immune-Mediated Inflammatory Diseases (SAFER)”, which included SLE patients vaccinated with CoronaVac, ChAdOx1, or BNT162b2. Patients with HIV infection, pregnant women, or those with immunosuppression not related to SLE were excluded. Safety data related to adverse events and underlying disease activity were assessed. Additionally, COVID-19 cases were monitored throughout the follow-up period. Results: The study included 373 patients with systemic lupus erythematosus (SLE), with a mean age of 36 years, the majority being women (89.8%). The most common adverse events after SARS-CoV-2 vaccination were injection site reactions and headache, observed both after the first and subsequent doses. The ChAdOx-1 vaccine was associated with a higher frequency of adverse events compared to CoronaVac. At baseline, 38.3% of patients were in remission, 32.8% had low disease activity, and 28.9% had moderate to high activity. Following CoronaVac vaccination, there was an increase in remission rates (from 34.6% to 51.1%) and a significant reduction in moderate to high activity (from 37.6% to 15.0%) after the first dose, with this reduction partially maintained after the second dose. In contrast, patients vaccinated with ChAdOx-1 showed an increase in moderate to high activity (from 14.5% to 38.2% after the first dose), a trend that persisted after the second dose. No statistically significant changes in disease activity were observed among those who received BNT162b2. During follow-up, 44 cases of COVID-19 were reported, all mild, with no deaths or need for intensive care unit admission. Conclusions: Vaccination against SARS-CoV-2 demonstrated a favorable safety profile in patients with SLE, with a low frequency of serious adverse events. While analysis of disease activity revealed variations across vaccine platforms, most notably an increased proportion of moderate to high disease activity among those receiving ChAdOx-1 compared with CoronaVac and BNT162b2, the overall occurrence of COVID-19 during follow-up was limited to mild cases, with no severe outcomes. These findings highlight that, despite potential risks of disease exacerbation, the clear protection against severe COVID-19 supports vaccination as a beneficial strategy for this immunocompromised population. Full article

Throughout the 2019 coronavirus disease pandemic, various vaccine regimens were implemented. Real-world data comparing their effectiveness during the BA.1/BA.2 Omicron wave remain limited. We prospectively enrolled healthcare workers who had completed two doses of mRNA or ChAdOx1 (A) vaccine and received an mRNA vaccine booster (BNT162b2 (P) or mRNA-1273 (M)). Neutralizing antibody levels were measured 6 months after the primary vaccinations and 1 month post-booster vaccination using a surrogate virus neutralization assay. Breakthrough infections were identified through institutional surveillance and the national reporting system. Among 318 participants (P-P-P: 71; A-A-P: 205; A-P-P: 19; M-M-M: 23), pre-booster neutralizing activity was lowest in the ChAdOx1-primed groups. One month post-booster vaccination, the neutralizing activity exceeded 97% across all regimens. The cumulative incidence of breakthrough infection varied significantly from 43.7% (P-P-P) to 84.2% (A-P-P). In adjusted Cox models, A-P-P showed the highest infection risk (HR 2.99, 95% CI 1.65–5.42). In summary, mRNA boosters restored neutralizing activity, but during the early BA.1/BA.2 Omicron wave they were less effective in preventing infections regardless of disease severity. Therefore, antibody titers alone are insufficient for evaluating protection, underscoring the need for continuous monitoring to support timely policy decisions during epidemic surges. Full article

Background: In the Kingdom of Saudi Arabia, various COVID-19 vaccines were administered during the pandemic. However, region-specific real-word comparative data on their immunogenicity remain limited. This study aimed to assess the serological responses to Pfizer-BioNTech (BNT162b2), Moderna (mRNA-1273), and AstraZeneca (ChAdOx1 nCoV-19) vaccines in a diverse population living in KSA. Methods: This observational study included 236 adults recruited from vaccination sites in Riyadh. Participants provided serum samples at predefined intervals: before the first dose, after the first dose, after the second dose, and post-vaccination infection (if applicable). IgG and neutralising antibodies were quantified using ELISA assays. Demographic and vaccination data, and their associations with antibody responses, were evaluated. Results: At baseline, 75.4% of participants were positive for SARS-CoV-2 IgG, suggesting high prior exposure. Marked incremental increases in IgG levels were observed after each vaccine dose. Both Moderna and Pfizer elicited stronger responses, with Pfizer inducing the strongest early response and Moderna achieving the highest overall titres. Among IgG-positive individuals, neutralising antibodies were detected in 98.1%. There were no statistically significant differences by age or gender, although males tended to show higher mean titres. Heterologous vaccine schedules induced comparable or enhanced immunogenicity relative to homologous schedules, supporting their use in flexible immunisation strategies. Conclusions: All COVID-19 vaccines administered in Saudi Arabia elicited robust antibody responses, particularly the mRNA-based vaccines. Our findings support their continued use and justify varied vaccination approaches, including mix-and-match booster strategies, to enhance community immunity. Full article

RNA-based therapeutics offer transformative potential for treating devastating diseases. However, current RNA delivery technologies face significant hurdles, including inefficient tissue targeting, insufficient selectivity, and severe side effects, leading to the termination of many clinical trials. This review critically assesses the landscape of RNA-derived medicines, examining world-renowned mRNA vaccines (Spikevax, BNT162b2/Comirnaty) and RNA-based therapeutics like Miravirsen (anti-miR-122). It details the composition and clinical trial results of numerous modified short RNA drugs (e.g., siRNAs, miRNA mimetics/inhibitors) targeting various conditions. Prospects for RNA-based medicines are analysed for diseases with substantial societal impact, such as cancer, autoimmune disorders, and infectious diseases, with a focus on evolving delivery methods, including lipid nanoparticles, viral vectors, and exosomes. RNA-mediated macrophage reprogramming emerges as a promising strategy, potentially enhancing both delivery and clinical efficacy. This review highlights that while approved RNA therapies primarily target rare diseases due to delivery limitations, novel approaches in RNA modification, targeted delivery systems, and enhanced understanding of molecular mechanisms are crucial for expanding their application to prevalent diseases and unlocking their full therapeutic potential. Full article

Background/Objectives: Understanding the durability of immunity induced by mRNA COVID-19 vaccines, especially in individuals with chronic health conditions, remains essential for guiding booster strategies. We conducted a longitudinal study to evaluate humoral and cellular immune responses up to 21 months after a primary two-dose BNT162b2 vaccination followed by a booster, either homologous (BNT162b2) or heterologous (mRNA-1273). Methods: Twenty-eight adults, mostly with chronic conditions, were assessed at approximately 9, 12 and 21 months post-primary vaccination. Serum anti-trimeric Spike IgG levels were quantified, and peripheral blood mononuclear cells were analyzed at 21 months for Spike-specific memory B-cell and T-cell responses by flow cytometry. Results: Participants were stratified by booster type, prior SARS-CoV-2 infection and health status. Anti-Spike IgG persisted in all participants but declined over time. The heterologous mRNA-1273 booster induced higher antibody titers at 9 months, while the homologous BNT162b2 booster led to more sustained antibody levels and higher frequencies of Spike-specific memory B cells at 21 months. Prior infection significantly enhanced antibody titers, particularly in homologous booster recipients. Surprisingly, individuals with chronic health conditions exhibited equal or higher antibody levels compared to healthy participants at all time points. At 21 months, robust Spike-specific class-switched memory B cells and polyfunctional CD4⁺ and CD8⁺ T-cell responses were detected. Conclusions: These findings demonstrate that BNT162b2 vaccination elicits durable, multi-layered immunity lasting nearly two years, even in individuals with chronic conditions, and support the use of both homologous and heterologous mRNA boosters to sustain protection in diverse populations. Full article